1. Field of the Invention
This invention relates generally to apparatus used in connection with the drilling and servicing of earth boreholes. With more particularity, this invention relates to apparatus to be used in the manipulation of downhole equipment in earth boreholes commonly called xe2x80x9cwells,xe2x80x9d whether open or cased boreholes. With still further particularity, this invention relates to a hydraulically actuated downhole coupler system which permits coupling and decoupling of downhole tool components, and is especially (although not exclusively) adapted for coupling, then decoupling at a desired time, a washover assembly to and from a workstring comprising a fishing tool such as a spear or overshot grapple.
2. Description of Related Art
Almost all oil and natural gas production is from earthen boreholes, commonly called xe2x80x9cwells,xe2x80x9d which are drilled into a subterranean reservoir containing oil and/or natural gas. Wells are drilled with surface locations both onshore and offshore, and are today drilled in water depths of thousands of feet. The depths of the wells themselves may be many thousands of feet (quite commonly in excess of 10,000 feet, and as much as 20,000 feet) below the surface, whether ground or seafloor level. The geometry of such wells is appreciated when it is considered that a wellbore, for the sake of example having an inner diameter of 8-xc2xdxe2x80x3, and a depth of 10,000 feet, has the relative proportions of a typical wooden pencil approximately 295 feet long.
It may further be readily appreciated that it is oftentimes difficult to manipulate equipment and tools downhole, via actions taken at the surface, many thousands of feet away. Where possible, manipulation of downhole tools via hydraulic means (by applying fluid pressure at the surface), rather than by purely mechanical means, is often desirable.
The term xe2x80x9cfishxe2x80x9d is commonly used in connection with wells (including wells being drilled and after being completed) to refer to downhole equipment which is either unintentionally left in the hole, for example as a result of an equipment failure or from becoming stuck downhole; or to refer to downhole equipment which was intentionally put into place at one time, but is now sought to be removed. A xe2x80x9cfishing tool,xe2x80x9d then, refers to equipment employed to latch onto a fish to remove it from a well. Fishing tools are usually run into a well on the lower end of a string of drill pipe or tubing workstring, which is a string of threaded and coupled pipe of sufficient length to reach the downhole objective depth. For purposes of this patent application, the term xe2x80x9cdrillstringxe2x80x9d will be used to refer to either drill pipe or tubing. Some fishing tools are spears, which enter an inner bore of a fish (for example, the bore of a piece of pipe); others are grapples or xe2x80x9covershots,xe2x80x9d which have a bore large enough for the fish to enter the overshot bore, or said another way, the overshot engulfs the fish to connect or latch onto it.
Another condition which must often be addressed in retrieval of a fish is removal of material which has settled into a gap or annulus between the fish and the wall of the casing or open borehole. Such material may be formation solids such as sand and clay; or may be materials introduced into the wellbore, such as cement; or may be small pieces of fish such as steel cuttings which have settled in about the larger fish. The effect of such material when packed in around a fish is to firmly lodge the fish in place, and to retrieve the fish the material must be removed from the fish/wellbore annulus. Removal may be by a process called xe2x80x9cwashing over,xe2x80x9d which uses xe2x80x9cwashpipexe2x80x9d having a cutting or milling bottom edge (commonly called a xe2x80x9crotary shoexe2x80x9d), the washpipe having inner and outer diameters which permit it to pass through the annulus between the fish and the wellbore. By rotation of the washpipe and the rotary shoe and pumping of fluids (whether drilling mud or completion fluids), the material lodging the fish in place can then be removed. The remaining task is to latch onto the fish with a spear or overshot and pull the fish from the well.
An exemplary situation in which washover and then fishing operations are required is the retrieval of downhole sand control assemblies, commonly called a xe2x80x9cgravel pack,xe2x80x9d from a well. Certain producing formations have a tendency to flow not only formation fluids (oil and gas) but also sand from the formation, which is undesirable and potentially dangerous. A typical gravel pack assembly comprises a first or bottom packer (which is usually a permanent packer, not readily retrieved) which is set in the wellbore below the formation to be produced; a screen and blank pipe assembly which is stabbed into the first packer (referred to as a xe2x80x9cscreen assemblyxe2x80x9d); and a second or top packer (which is usually a retrievable packer that can be later released and pulled from the well) at the top of the screen assembly. A piece of the blank pipe between the screen and the top packer forms a xe2x80x9csafety subxe2x80x9d or xe2x80x9csafety jointxe2x80x9d and is configured so that it may be relatively easily separated by pulling it apart. Once the screen assembly is in place, a slurry of a carrying fluid and a relatively coarse sand or xe2x80x9cgravelxe2x80x9d is placed into the annulus between the outside of the screen and the inner wall of the casing and into the perforations. The gravel acts as a filter, permitting fluid flow from the formation but preventing sand production.
For various reasons, it may be desirable to work over or recomplete a gravel packed well and to do so retrieval of the gravel pack assembly (that is, the top packer and blank pipe and screen assembly) is required. Two required actions to permit retrieving the total assembly are (1) removal of the top packer, and (2) washing away the gravel in the screen/casing annulus which tends to be very firmly packed and therefore xe2x80x9clocksxe2x80x9d the screen assembly in place, and thereafter latching onto and retrieving the blank pipe and screen assembly.
With conventional xe2x80x9cseparatexe2x80x9d fishing tools, to retrieve the top packer, wash over the screen assembly, then pull the screen assembly from the hole, typically three downhole tool runs are required:
1. Run #1 with a packer retrieving tool. This tool locks into the top packer, and pulling on the tool releases the packer from its grip on the casing wall. Continued pulling then separates the safety sub, and the top packer with a short piece of the blank pipe attached is then pulled from the well.
2. Run #2 with a washpipe assembly, to wash over the screen assembly and remove the gravel in the screen/casing annulus.
3. Run #3 with an overshot or spear to engage the uppermost section of the blank pipe/screen assembly and pull it from the well.
Considerable benefit arises out of combining steps 2 and 3 above. With deeper wells, the trip in and out of the well consumes a number of hours, and with overall daily costs at times exceeding $100,000 per day, a single trip might represent $100,000 in costs. In short, the ability to accomplish both the washover and fishing operation by a single trip in the well, with a combination washpipe and fishing tool assembly, is of great value. A combination washpipe and fishing tool assembly has the fishing tool (such as a spear or overshot) connected to the lower end of the drillstring, with the washpipe both longitudinally and rotationally fixed to the drillstring via a coupler system such that the fishing tool is disposed within the upper portion of the washpipe. At a selected time, the coupler system permits disconnecting the washpipe from a fixed position with respect to the drillstring, and permits the washpipe to ride up about the drillstring, with the fishing tool moving (in relative terms) downwardly within the washpipe to latch onto the fish.
The related art shows several tools which combine a washover and fishing assembly, coupled together via mechanical means so that first the washover assembly can be employed, then the fishing assembly employed to latch onto and then retrieve the fish. Different mechanical means for connecting and then selectively disconnecting the washover and fishing tool assemblies disclosed in the related art include simple set screws which are sheared to disconnect, such as in U.S. Pat. No. 5,810,410 to Arterbury et al, Sep. 22, 1998 and U.S. Pat. No. 5,887,925 to Arterbury et al, Mar. 30, 1999; and a J-latch assembly, such as in U.S. Pat. No. 3,785,690 to Hutchinson, Jan. 15, 1974. Other examples of washover/fishing tool apparatus are U.S. Pat. No. 3,747,674 to Murray, Jul. 24, 1973; and U.S. Pat. No. 4,877,085 to Pullig, Jr., Oct. 31, 1989.
The known related art does not disclose a downhole tool comprising a hydraulically actuated coupler system which initially couples a washover assembly to a drillstring/fishing tool assembly, then at a desired time, via hydraulic operation, uncouples the two assemblies so that the washover assembly may move upwardly about the drillstring and the fishing tool lowered and employed to engage the fish.